JP2008216294A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of forming a nip part of long nip width and high adhesion and capable of preventing nonuniform gloss from occurring on an image obtained by fixing. <P>SOLUTION: The fixing device includes: an endless fixing belt 43 rotated while kept extended between a plurality of support members; and a pressure roller 42 that forms a nip part N in contact with the peripheral face of the fixing belt 43. The plurality of support members include: a fixing roller 41 disposed opposite the pressure roller 42 via the fixing belt 43; and a separation member 44 disposed downstream of the developing roller 41 in a paper conveyance direction P and separate from the fixing roller 41 and pressure roller 42. The nip part N includes a first nip area N1 located in contact with the fixing roller 41, and a second nip area N2 located downstream of the first nip area N1 in the paper conveyance direction P so as to be continuous with the first nip area N1. In the fixing device 40, the width of the first nip area N1 is equal to or greater than the width of the second nip area N2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is applied to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, and a multi-function machine thereof, and a fixing device for fixing an unfixed toner image transferred onto a sheet to the sheet. And an image forming apparatus including the fixing device.

  An image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, and a multifunction machine of these includes a fixing device that performs a fixing process for fixing an unfixed toner image transferred onto a sheet to the sheet. ing. In general, a fixing device includes a fixing roller that heats a sheet, and a pressure roller that has a circumferential surface opposed to the circumferential surface of the fixing roller, and a nip between the two rollers. The fixing process is performed by passing the sheet on which the unfixed toner image is transferred to the part.

  Since such a fixing device has a short nip width, the fixing device needs to be fixed at a high fixing temperature in order to provide a heat amount necessary for a fixing process in which unfixed toner is melted and fixed on a sheet. However, when the fixing process is performed at a high fixing temperature, a so-called high temperature offset phenomenon occurs in which toner adheres to the fixing roller at the end of the nip portion. This is because when a toner is melted at a high fixing temperature, a low-melting toner such as a color toner has a greatly reduced viscosity, and the adhesion force between toners (cohesion between toners) is greatly reduced. This is because the adhesive force between the roller and the toner exceeds the cohesive force between the toners.

  In the case of color printing using a plurality of color toners, a plurality of color toners overlap so that the toner image becomes thick. Therefore, the temperature of the toner image on the side in contact with the fixing roller and the toner on the side in contact with the paper A large temperature difference occurs between the image temperature and the toner image cannot be uniformly melted.

  Therefore, in order to give a necessary amount of heat to the toner at a relatively low fixing temperature over a long time, a fixing device having a long nip width has been proposed. For example, an elastic layer is provided on the surfaces of the pressure roller and the fixing roller, and the elastic layer is deformed by pressure contact with the pressure roller and the fixing roller, so that a long nip width is secured, and further, the shape of the deformed nip portion is obtained. Based on this, there is a fixing device that separates the sheet from the fixing roller. In such a fixing device, the thicker the elastic layer, the longer the nip width can be secured. However, when a thick elastic layer is provided on the fixing roller, the surface of the fixing roller is caused by the low thermal conductivity of the elastic layer. The waiting time until the toner reaches the toner fixing temperature, so-called warm-up time, becomes longer. Further, the temperature followability at the time of continuous paper feeding is deteriorated, uneven heat supply to the toner image is generated, and uneven gloss is generated in the fixed image.

  In order to solve the above problem, a technique for fixing a toner image on a sheet using a belt has been proposed. For example, an endless fixing belt that is stretched between a fixing roller and a driven roller, and a pressure roller that faces the fixing roller via the fixing belt, and is conveyed in a state where the sheet is in contact with the fixing belt. A fixing device configured as described above is known (see Patent Document 1). Furthermore, in a fixing device configured to convey such paper in contact with the fixing belt, the fixing belt is configured with a conductive member as a base, and the fixing roller has a polarity opposite to the voltage applied to the transfer unit. A fixing device that applies the above voltage has been proposed (see Patent Document 2).

Further, a fixing device 101 as shown in FIG. 7 has been proposed. FIG. 7 is a schematic cross-sectional view illustrating a configuration of a conventional fixing device 101. FIG. 7A shows the overall configuration of the fixing device 101, and FIG. 7B shows an enlarged view of the periphery of the driven roller 102 of the fixing device 101. The fixing device 101 includes an endless fixing belt 104 that is spanned between a fixing roller 103 and a driven roller 102, and a pressure roller 105 that faces the fixing roller 103 via the fixing belt 104. The fixing belt 104 is wound around the pressure roller 105 by pressing the driven roller 102 against the pressure roller 105 via the fixing belt 104 on the downstream side in the paper conveyance direction P of the roller 103 (Patent Document). 3 and Patent Document 4).
JP-A-4-284482 JP-A-9-190099 JP 2000-89593 A JP 2003-337488 A

  According to Patent Document 1, a first nip region formed by pressure contact between a fixing roller and a pressure roller and a second nip region formed by contact conveyance between a fixing belt and a sheet are formed as a nip portion. It has been proposed that a long nip is formed. However, in the second nip region, only the sheet and the fixing belt are in contact with each other, and no force is applied to the sheet and the fixing belt so that the adhesion between the fixing belt and the sheet is very low. If the adhesion between the fixing belt and the paper is low as described above, uneven heat supply from the fixing belt to the paper occurs, and uneven gloss occurs in the image obtained by fixing.

  According to Patent Document 2, it is described that an electrostatic force acts between the paper and the fixing belt in the second nip region, so that the adhesion between the paper and the fixing belt can be improved. However, the electrostatic force is weaker than the physical pressing force, and the adhesion between the fixing belt and the paper cannot be increased to the extent that the occurrence of uneven heat supply from the fixing belt to the paper can be suppressed.

  In addition, as shown in FIG. 7A, the fixing device 101 described in Patent Document 3 and Patent Document 4 includes, as a nip portion N, a first nip region N1 in which the fixing roller 103 is in contact, and the nip portion N1. A second nip region N2 is formed. The second nip region N2 is a region that continues from the end of the first nip region N1 to the pressure contact portion between the driven roller 102 and the pressure roller 105. The second nip region N <b> 2 is formed when the pressure roller 105 presses the driven roller 102 via the fixing belt 104. For these reasons, it is disclosed that the fixing device 101 can form a nip portion having a long nip width and a pressing force. However, in actuality, as shown in FIG. 7B, the fixing belt 104 is bent in the second nip region N2 so that the fixing belt 104 is separated from the pressure roller 105, that is, a so-called pressure release occurs. Thus, an area where the adhesion between the paper P and the fixing belt 104 is lowered is formed.

  Accordingly, the present invention provides a fixing device that can form a nip portion having a long nip width and high adhesion, and that can prevent occurrence of uneven gloss in an image obtained by fixing, and this fixing device. An object is to provide an image forming apparatus provided.

  The fixing device of the present invention includes: an endless fixing belt that is stretched over a plurality of support members; and a pressure roller that abuts on an outer peripheral surface of the fixing belt to form a nip portion. The support member includes a fixing roller that faces the pressure roller via the fixing belt, and separation of the paper that is provided on the downstream side in the paper conveyance direction from the fixing roller and separated from the fixing roller and the pressure roller. The nip portion includes a first nip region N1 that contacts the fixing roller, and a second nip region N2 that continues downstream of the first nip region N1 in the sheet conveying direction. The fixing device is characterized in that the width of the nip region N1 is equal to or greater than the width of the second nip region N2.

  According to this configuration, the nip portion formed by bringing the pressure roller into contact with the outer peripheral surface of the fixing belt includes the first nip region N1 in contact with the fixing roller and the sheet conveyance direction of the first nip region N1. And a second nip region N2 following the downstream side. The first nip region N1 is a region where the fixing roller and the pressure roller are in pressure contact with each other via the fixing belt, and corresponds to a nip portion of a conventional fixing device that does not use a belt. Since the nip portion in the present invention includes not only the first nip region N1 but also the second nip region N2, a nip portion having a long nip width can be formed without providing an elastic layer on the fixing roller.

  The second nip area N2 is an area in which the outer peripheral surface of the fixing belt comes into contact with the pressure roller by separating the fixing belt from the fixing roller by a sheet separating member. Therefore, in the second nip region N2, the fixing belt is pressed against the pressure roller by the sheet separating member. Further, since the paper separating member is provided apart from the fixing roller and the pressure roller, the second nip region is formed without the paper separating member being pressed against the pressure roller via the fixing belt. Yes. Therefore, it is possible to suppress the occurrence of the bending of the fixing belt, that is, the so-called pressure loss in the second nip region N2.

  Further, since the width of the first nip area N1 is equal to or larger than the width of the second nip area N2, the sheet is conveyed through the second nip area N2 while maintaining the toner temperature in the first nip area N1. it can. Accordingly, the second nip region N2 can help the toner adhere to the fixing belt by the adhesive force of the toner to the fixing belt, and can improve the adhesion between the paper and the fixing belt. Furthermore, since the toner temperature drop in the second nip region N2 can be suppressed, the sheet can be separated from the fixing belt at an appropriate toner temperature.

  As described above, the fixing device of the present invention can form a nip portion having a long nip width and high adhesion, and can prevent uneven glossiness from occurring in an image obtained by performing the fixing process.

  In the fixing device, it is preferable that a radius of curvature of the fixing belt at a portion in contact with the separation member is smaller than a radius of the fixing roller. According to this configuration, the direction in which the fixing belt travels greatly changes at the portion where the fixing belt is in contact with the separation member. Therefore, even if the adhesion between the paper and the fixing belt is high, the paper is removed from the fixing belt by the waist of the paper and its own weight. Easy to peel off.

  It is preferable that the fixing roller is a heating roller that heats the fixing belt. According to this configuration, since the fixing roller directly heats the first nip region N1 in contact with the fixing roller, the thermal efficiency is high. Further, since the fixing roller also serves as a heating roller, it is not necessary to provide a heating roller separately from the fixing roller, so that space can be saved.

  The plurality of support members include the fixing roller as an elastic roller and a heating roller, the fixing belt is stretched over the fixing roller, the heating roller, and the separation member, and the heating roller is It is preferable to heat the fixing belt. According to this configuration, since the heating roller is provided separately from the fixing roller, an elastic roller suitable for the fixing process can be used as the fixing roller.

  It is preferable that the width of the first nip region N1 is not more than twice the width of the second nip region N2. According to this configuration, the toner can be sufficiently melted in the first nip region N1 and the effect of assisting the toner in close contact with the fixing belt in the second nip region N2 can be sufficiently exhibited. Can form a higher nip.

  In the fixing device, it is preferable that the separation member is a fixed guide member having a sliding contact surface that is in sliding contact with the fixing belt. Since such a separating member can be brought close to the end of the second nip region N2, the second nip region N2 can be easily set to a suitable nip width, and further space saving can be achieved. In addition, the radius of curvature of the fixing belt in contact with the separation member can be set to be small, which can contribute to stabilization of separation and conveyance, and suppression of occurrence of offset phenomenon and image disturbance due to an increase in peeling speed.

  It is preferable that the separation member is a driven roller that rotates following the rotation of the fixing belt. Such a separating member has a reduced sliding load and can suppress damage to the fixing belt and the separating member.

  It is preferable that a difference between the first temperature of the fixing belt at the start end of the nip portion and the second temperature of the fixing belt at the separation / contact position of the sheet by the separation member is less than 10 ° C. As described above, when the temperature difference between the first temperature and the second temperature is small, the adhesive force of the toner to the fixing belt can be maintained in the second nip region N2, so that the adhesion between the sheet and the fixing belt can be ensured. Further, since the temperature decrease of the fixing belt is small, the toner temperature is also hardly decreased, and the sheet can be separated from the fixing belt at an appropriate toner temperature.

  It is preferable that the fixing belt is a member having a large heat capacity because temperature decrease of the fixing belt is reduced. In particular, the fixing belt is preferably a belt made of a member including a nickel layer or a member having a silicone rubber layer on the surface.

  It is preferable that the separation member is a member made of a heat insulating material having a heat insulating property or a member covered with a heat insulating material having a heat insulating property. According to this configuration, it is possible to suppress a decrease in the temperature of the fixing belt due to the contact of the separation member.

  It is preferable that the pressure roller is a driving roller for driving the fixing belt. According to this configuration, in the second nip region N2, a force that the fixing belt follows the rotation direction of the pressure belt is applied, and this force becomes a force that closely contacts the sheet and the fixing belt. The adhesion between the paper and the fixing belt can be improved.

  An image forming apparatus of the present invention is an image forming apparatus using an electrophotographic system, and includes the fixing device. According to this configuration, the image forming apparatus enjoys the effect of the fixing device of the present invention, and gloss unevenness hardly occurs and a high-quality image can be formed on a sheet.

  The fixing device of the present invention can form a nip portion having a long nip width and high adhesion, and can prevent uneven glossiness from occurring in an image obtained by fixing. Accordingly, when the fixing device of the present invention is provided, an image forming apparatus that can form high-quality images with less uneven gloss is obtained.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of a fixing device of the present invention and an image forming apparatus including the fixing device will be described in detail with reference to the drawings. As an image forming apparatus, a tandem type image forming apparatus will be described as an example. However, any image forming apparatus using an electrophotographic method may be used, and the image forming apparatus is not limited to a tandem type image forming apparatus. Further, as a type of the image forming apparatus, a color printer will be described as an example. However, for example, a copying machine, a facsimile machine, and a multifunction machine may be used. Further, the image bearing member will be described by taking a photosensitive drum as a drum-shaped photosensitive member as an example. However, the image bearing member is not limited to this, and the belt-shaped photosensitive member, the sheet-shaped photosensitive member, etc. Is also applicable.

[First Embodiment]
First, a color printer as an example of an image forming apparatus to which a fixing device according to a first embodiment of the present invention is applied will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view showing the overall configuration of a color printer 1 including a fixing device 40 according to the first embodiment of the present invention.

  As shown in FIG. 1, the color printer 1 has a box-shaped device body 1a. In the apparatus main body 1a, a toner image based on image data and the like is transferred to the paper P while feeding the paper P fed from the paper feeding unit 2 and the paper P fed from the paper feeding unit 2. An image forming unit 3 and a fixing unit 4 for performing a fixing process for fixing the unfixed toner image transferred onto the paper P by the image forming unit 3 to the paper P are provided. Further, on the upper surface of the apparatus main body 1a, a paper discharge unit 5 for discharging the paper P subjected to the fixing process by the fixing unit 4 is provided.

  The paper feed unit 2 includes a paper feed cassette 21, a pickup roller 22, paper feed rollers 23, 24, 25 and a registration roller 26. The paper feed cassette 21 is provided so as to be detachable from the apparatus main body 1a, and stores the paper P of each size. The pickup roller 22 is provided at the upper right position of the paper feed cassette 21 shown in FIG. 1 and takes out the paper P stored in the paper feed cassette 21 one by one. The paper feed rollers 23, 24 and 25 send out the paper P taken out by the pickup roller 22 to the paper transport path. The registration roller 26 temporarily waits for the paper P sent to the paper transport path by the paper feed rollers 23, 24, 25, and then supplies it to the image forming unit 3 at a predetermined timing.

  The paper feeding unit 2 further includes a manual feed tray (not shown) and a pickup roller 27 that are attached to the right side surface of the device main body 1a shown in FIG. The pickup roller 27 takes out the paper P placed on the manual feed tray. The paper P taken out by the pickup roller 27 is sent out to the paper conveyance path by the paper feed rollers 23 and 25 and is supplied to the image forming unit 3 by the registration roller 26 at a predetermined timing.

  The image forming unit 3 includes an image forming unit 7, an intermediate transfer belt 11 on which a toner image based on image data transmitted from a computer or the like to the surface (contact surface) of the image forming unit 7 is primarily transferred, A secondary transfer roller 12 is provided for secondary transfer of the toner image on the intermediate transfer belt 11 to the paper P fed from the paper feed cassette 21.

  The image forming unit 7 includes a black unit 7K, a yellow unit 7Y, a cyan unit 7C, and a magenta unit 7M, which are sequentially arranged from the upstream side (left side in FIG. 1) to the downstream side. I have. In each of the units 7K, 7Y, 7C, and 7M, a photosensitive drum 71 as an image carrier is arranged at the center position so as to be rotatable in the direction of an arrow (counterclockwise). Around each photosensitive drum 71, a charger 75, an exposure device 76, a developing device 72, a cleaning device 73, a static eliminator 74, and the like are sequentially arranged from the upstream side in the rotation direction.

  The charger 75 uniformly charges the peripheral surface of the photosensitive drum 71 rotated in the direction of the arrow. Examples of the charger 75 include a scorotron charger. The exposure device 76 is a so-called laser scanning unit, which irradiates the peripheral surface of the photosensitive drum 71 uniformly charged by the charger 75 with laser light based on image data input from an image reading device or the like. An electrostatic latent image based on the image data is formed on the drum 71. The developing device 72 supplies toner to the peripheral surface of the photosensitive drum 71 on which the electrostatic latent image is formed, thereby transferring the toner image based on the image data. The toner image is primarily transferred to the intermediate transfer belt 11. The cleaning device 73 cleans the toner remaining on the peripheral surface of the photosensitive drum 71 after the primary transfer of the toner image to the intermediate transfer belt 11 is completed. The neutralizer 74 neutralizes the peripheral surface of the photosensitive drum 71 after the primary transfer is completed. The peripheral surface of the photosensitive drum 71 cleaned by the cleaning device 73 and the static eliminator 74 is directed to the charger 75 for a new charging process, and a new primary transfer is performed.

  The intermediate transfer belt 11 is an endless belt-like rotating body, and includes a driving roller 13, a driven roller 14, a backup roller 15, a primary roller such that the surface (contact surface) side is in contact with the peripheral surface of each photosensitive drum 71. It is stretched over a plurality of rollers such as a transfer roller 16 and a tension roller 17. Further, the intermediate transfer belt 11 is configured to rotate endlessly by the plurality of rollers in a state where the intermediate transfer belt 11 is pressed against the photosensitive drum 71 by a primary transfer roller 16 disposed to face each photosensitive drum 71. The driving roller 13 is rotationally driven by a driving source 18 such as a stepping motor, and gives a driving force for rotating the intermediate transfer belt 11 endlessly. The driven roller 14, the backup roller 15, the primary transfer roller 16, and the tension roller 17 are rotatably provided, and are driven to rotate with the endless rotation of the intermediate transfer belt 11 by the driving roller 13. These rollers 14, 15, 16, and 17 are driven to rotate via the intermediate transfer belt 11 according to the main rotation of the driving roller 13 and support the intermediate transfer belt 11. The tension roller 17 applies tension (tension) to the intermediate transfer belt so that the intermediate transfer belt 11 does not loosen.

  The primary transfer roller 16 applies a primary transfer bias (a polarity opposite to the charging polarity of the toner) to the intermediate transfer belt 11. By doing so, the toner image formed on each photoconductive drum 71 circulates in the arrow (clockwise) direction between each photoconductive drum 71 and the primary transfer roller 16 by the drive roller 13. The intermediate transfer belt 11 is sequentially transferred (primary transfer) in an overcoated state.

  The secondary transfer roller 12 applies a secondary transfer bias having a polarity opposite to that of the toner image to the paper P. By doing so, the toner image primarily transferred onto the intermediate transfer belt 11 is transferred to the paper P between the secondary transfer roller 12 and the backup roller 15, and thereby, the color transfer image ( An unfixed toner image) is transferred.

  The fixing unit 4 performs a fixing process for fixing an untransferred toner image formed on the paper P by the image forming unit 3 to the paper P, and includes a fixing device 40. The fixing device 40 includes an endless fixing belt 43 that rotates around a plurality of support members such as a fixing roller 41 that is heated by an energizing heat generating member, and an outer peripheral surface of the fixing belt 43 that contacts the nip portion N. And a pressure roller 42 for forming the. The configuration of the fixing device 40 will be described in detail later. Then, the sheet P on which the non-transferred toner image is transferred by the secondary transfer roller 12 in the image forming unit 3 is sent toward the nip N formed between the fixing belt 43 and the pressure roller 42, By passing through the nip portion N, the untransferred toner image is fixed on the paper P by the fixing process by heat from the fixing roller 41. Then, the paper P subjected to the fixing process is discharged to the paper discharge unit 5. Further, in the color printer 1 of the present embodiment, a transport roller 6 is disposed at an appropriate position between the fixing unit 4 and the paper discharge unit 5.

  The paper discharge unit 5 is formed by recessing the top of the apparatus main body 1a of the color printer 1, and a paper discharge tray 51 for receiving the discharged paper P is formed at the bottom of the concave portion. .

  Next, the configuration of the fixing device 40 according to the first embodiment of the present invention will be described. FIG. 2 is a schematic cross-sectional view showing a configuration of the fixing device 40 according to the first embodiment of the present invention, and shows an enlarged configuration of the fixing device 40 provided in the color printer 1 shown in FIG. is there.

  The fixing device 40 includes a pressure roller 42, a fixing belt 43, a thermistor 46 that detects the outer peripheral surface temperature of the fixing belt 43, a front guide plate 47 that guides the paper P to the nip portion N, and a And a rear guide plate 48 for guiding the paper P to the outside.

  The fixing belt 43 is an endless belt, and a plurality of support members and pressure rollers 43 in a state where the fixing belt 43 is stretched over a plurality of support members of a fixing roller 41, a sheet separating member 44, and a tension roller 45. For example, it is configured to rotate endlessly. The nip portion N formed by contacting the pressure roller 42 with the outer peripheral surface of the fixing belt 43 includes a first nip region N1 that contacts the fixing roller 41, and a sheet conveyance direction P downstream of the first nip region N1. And a second nip region N2 that continues to the side. The first nip region N1 is a region where the fixing roller 41 and the pressure roller 42 are in pressure contact with each other via the fixing belt 43, and therefore corresponds to a nip portion of a conventional fixing device that does not use a belt. Since the nip portion in the present invention includes not only the first nip region N1 but also the second nip region N2, a nip portion having a long nip width can be formed without providing an elastic layer on the fixing roller 41.

  Further, it is preferable that the fixing belt 43 is a member having a large heat capacity in order to reduce a temperature drop of the fixing belt 43. The fixing belt 43 is not particularly limited, but is preferably made of a member including a nickel layer or a stainless steel layer, or a member having a silicone rubber layer on the surface. Preferable specific examples of the fixing belt 43 include, for example, a nickel belt as a core material, a silicone rubber layer as an elastic layer, and a fluororesin layer as a release layer, which are sequentially laminated from the nickel belt toward the outer peripheral surface. The thing comprised with these is mentioned. Examples of the fluororesin layer include polytetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) and polytetrafluoroethylene (PTFE), and PFA is preferably used. The fluororesin layer may be fluorinated using PFA or the like on the silicone rubber layer, but the PFA tube may be covered with a nickel belt and a silicone rubber layer.

  The thickness of the nickel belt is not particularly limited and is appropriately set depending on the situation, but is preferably 30 to 40 μm, and is set to 35 μm, for example. The thickness of the silicone rubber layer is not particularly limited and is appropriately set depending on the situation, but is preferably 400 to 800 μm, for example, 500 μm. The thickness of the fluororesin layer is not particularly limited and is appropriately set depending on the situation, but is preferably 30 to 70 μm, and is set to 50 μm, for example.

  The fixing roller 41 is disposed to face the pressure roller 42 with the fixing belt 43 interposed therebetween. The fixing roller 42 is not particularly limited, and includes, for example, a metal roller 81 having a fluororesin layer such as PFA as a release layer and a halogen lamp 82 as a heat source built in the metal roller 81. The The fixing roller 41 may include an elastic layer, but may not include the elastic layer. If the elastic body is not provided as in the present embodiment, the waiting time until the surface of the fixing belt 43 reaches the toner fixing temperature, so-called warm-up time, is shortened, and the temperature followability during continuous paper passing is good. It becomes.

  The material of the metal roller 81 is not particularly limited, and any metal can be used, but iron is preferably used. The thickness of the metal roller 81 is not particularly limited and is appropriately set depending on the situation, but is preferably 0.3 mm to 0.7 mm, for example, 0.5 mm.

  The halogen lamp 82 is an energization heating element that generates heat when power is supplied from a power supply (not shown) controlled by the temperature detected by the thermistor 46. The halogen lamp 82 only needs to be able to heat the fixing belt 43 to the extent that the toner image on the paper P can be fixed. For example, a 1000 W halogen lamp is used.

  The fixing roller 42 is a heating roller that heats the fixing belt 43 by heat transfer from the metal roller 81 heated by the radiant heat from the halogen lamp 82. When the fixing roller 41 is a heating roller, the fixing roller 41 directly heats the first nip region N1 in contact with the fixing roller 41, so that the thermal efficiency is high. Further, since the fixing roller 41 also serves as a heating roller, it is not necessary to provide a heating roller in addition to the fixing roller 41, so that space can be saved.

  Further, the outer diameter of the fixing roller 41 is not particularly limited, and is appropriately set according to the situation, but is preferably 30 to 50 mm, for example, 40 mm.

  The front separation member 44 is provided on the downstream side of the fixing roller 41 in the paper transport direction P and away from the fixing roller 41 and the pressure roller 42. Further, the separating member 44 is disposed such that the sliding contact surface with the fixing belt 43 is closer to the pressure roller 42 than the tangent line connecting the start end and the end end of the first nip region N1. The separation member 44 separates the fixing belt 43 from the fixing roller 41, and a portion where the pressure roller 42 is in contact with the outer peripheral surface of the fixing belt 43 is formed. This portion corresponds to the second nip region. That is, in the second nip region N2, the separating member 44 provided away from the fixing roller 41 and the pressure roller 42 is disposed closer to the pressure roller 42 than the tangent line connecting the start and end of the first nip region N1. This is a region formed by doing so. Therefore, since the fixing belt 43 is pressed against the pressure roller 42 by the separating member 44, the bending of the fixing belt 43 in the second nip region N2, that is, so-called pressure loss can be suppressed.

  The distance D between the separation / contact position of the paper P by the separation member 44 and the end of the nip portion N is preferably short. By doing so, the bending of the fixing belt 43 in the second nip region N2, that is, the occurrence of so-called pressure loss can be further suppressed.

  The separation member 44 is a fixed guide member having a sliding contact surface that is in sliding contact with the fixing belt 43. Since the separating member 44 can be brought close to the end of the second nip region N2, the distance D can be shortened to the sheet. The second nip region N2 can be easily set to a suitable nip width, and further space saving can be achieved. In addition, the radius of curvature of the fixing belt 43 in contact with the separation member 44 can be set to be small, which can contribute to stabilization of separation and conveyance, and suppression of occurrence of offset phenomenon and image disturbance due to an increase in peeling speed.

  The material of the separation member 44 is not particularly limited, but is preferably a member made of a heat insulating material having a heat insulating property or a member covered with a heat insulating material having a heat insulating property. The temperature drop of the fixing belt 43 due to the contact of the separation member 44 can be suppressed. As a preferable specific example of the separating member 44, for example, a material in which stainless steel (SUS) is coated with a sheet in which a nomex felt made of an aramid resin and a fluorine-impregnated glass cloth are bonded to each other can be cited.

  Further, the radius of curvature of the fixing belt 43 in contact with the separation member 44 is smaller than the radius (outer diameter) of the fixing roller 41. As a result, the direction in which the fixing belt 43 travels greatly changes at the portion where the fixing belt 43 contacts the separation member 44. Therefore, even if the adhesion between the paper P and the fixing belt 43 is high, the paper P is loaded by the waist and weight of the paper P. It can be easily peeled off from the fixing belt 43.

  The tension roller 45 applies tension to the fixing belt 43 so that the fixing belt 43 does not slack. The tension roller 45 can further suppress the bending of the fixing belt 43 in the second nip region N2, that is, the so-called pressure loss. Further, it is preferable that the tension roller 45 is rotatably provided and is driven to rotate as the fixing belt 43 rotates endlessly. Such a tension roller 45 can reduce a sliding load and suppress damage to the fixing belt 43. The outer diameter of the tension roller 45 is not particularly limited and is appropriately set depending on the situation, but is preferably 10 to 15 mm, for example, 12 mm. The material of the tension roller 45 is not particularly limited, and examples thereof include a material in which the surface of SUS is ceramic coated.

  The thermistor 46 is a temperature sensor that contacts the outer peripheral surface of the portion of the fixing belt 43 that is in contact with the fixing roller 41 and detects the outer peripheral surface temperature of the fixing belt 43. The thermistor 46 is not particularly limited. For example, the thermistor 46 is a ceramic semiconductor made of a metal oxide as a main raw material and sintered at a high temperature. The thermistor 46 has a negative temperature coefficient that decreases as the temperature increases. The halogen lamp 82 is controlled by an unillustrated control unit based on a signal related to the outer peripheral surface temperature of the fixing belt 43 detected by the thermistor 46, and the supplied electric power is adjusted so that the outer peripheral surface temperature of the fixing belt 43 is a predetermined value. Controlled to maintain temperature.

  The pressure roller 42 is pressed against the outer peripheral surface of the fixing belt 43 to form a nip portion N. Preferable specific examples of the pressure roller 42 include, for example, a metal roller 83 as a core material, a silicone rubber layer 84 as an elastic layer, which is sequentially laminated toward the outer peripheral surface of the metal roller 83, and a release layer. And a halogen lamp 85 built in a metal roller 83. The material of the metal roller 83 is not particularly limited, and any metal can be used, but aluminum is preferably used. Examples of the fluororesin layer include PFA and PTFE, and PFA is preferably used. The fluororesin layer may be fluorinated using PFA or the like on the silicone rubber layer 84, but a PFA tube may be covered on the silicone rubber layer 84. The outer diameter of the pressure roller 42 is not particularly limited and is appropriately set depending on the situation, but is preferably 20 to 40 mm, and is set to 30 mm, for example. The thickness of the silicone rubber layer 84 is not particularly limited and is appropriately set depending on the situation, but is preferably 2 to 4 mm, for example, 3 mm. The thickness of the fluororesin layer is not particularly limited and is appropriately set depending on the situation, but is preferably 30 to 70 μm, and is set to 50 μm, for example.

  The halogen lamp 85 suppresses the temperature drop of the fixing belt 43 caused by the pressure roller 42 coming into contact with the fixing belt 43, and further assists the fixing process for the toner image on the paper P by the heat from the halogen lamp 85. . As the halogen lamp 85, for example, a lamp of 300 W is used.

  In addition, the pressure roller 42 is driven to rotate about the axis when the driving force of a drive motor (not shown) is transmitted. In the pressure roller 42, the driving rotation is transmitted to the fixing belt 43 that is in pressure contact with the pressure roller 42, whereby the fixing belt 43 is a driving roller that circulates between the heating roller 42 and the fixing roller 41. Since the pressure roller 42 is a driving roller, a force that the fixing belt follows the rotation direction of the pressure belt is applied in the second nip region N2, and this force is a force that brings the paper and the fixing belt into close contact with each other. The adhesion between the sheet and the fixing belt in the 2-nip region N2 can be improved.

  The front guide plate 47 is arranged in the vicinity of the starting end of the nip portion N at the rear end, and guides the paper P to the nip portion N so that the lower surface of the paper P is supported along the rotation direction of the fixing belt 43. The rear guide plate 48 is a separation plate that prevents the paper P from being conveyed toward the fixing belt 43 and guides the paper P from the nip portion N to the outside. The distances between the front guide plate 47 and the rear guide plate 48 and the fixing belt 43 are not particularly limited, and are set as appropriate according to the situation. For example, the distance is set to 0.5 mm. Moreover, the material of the front guide plate 47 and the rear guide plate 48 is not particularly limited. For example, a material obtained by winding a SUS surface with a PFA tape is used.

  A nip portion N formed between the fixing belt 43 and the pressure roller 42 includes a first nip region N1 that contacts the fixing roller 41 and a second nip that continues downstream of the first nip region N1 in the sheet conveyance direction P. The width of the first nip region N1 is longer than the width of the second nip region N2. That is, the width of the first nip region N1 is equal to or greater than the width of the second nip region N2. Accordingly, the sheet P can be conveyed through the second nip region N2 while maintaining the toner temperature in the first nip region N1. Then, in the second nip region N2, not only the fixing belt 43 is pressed against the pressure roller 42 by the separation member 44 and the adhesion between the paper P and the fixing belt is improved, but also the adhesive force of the toner to the fixing belt 43 is increased. As a result, it is possible to assist the toner in intimate contact with the fixing belt 43 and improve the adhesion between the paper P and the fixing belt 43. This is considered to be based on the relationship between the adhesive force between the toner and the fixing belt 43 and the toner temperature.

  FIG. 3 is a schematic diagram showing the relationship between the adhesive force between the toner and the fixing belt and the toner temperature. The vertical axis indicates the adhesive force of the toner to the fixing belt, and the horizontal axis indicates the toner temperature. As shown in FIG. 3, if the toner temperature is too low, the adhesive force between the toner and the fixing belt is remarkably reduced. On the other hand, if the toner temperature is too high, the adhesive force between the toner and the fixing belt is reduced.

  When the relationship between the first nip region N1 and the second nip region N2 is as in the present invention, a decrease in toner temperature in the second nip region N2 can be suppressed. Therefore, if the toner temperature in the first nip region N1 is near the toner temperature T where the adhesive force between the toner and the fixing belt is strong, the toner temperature is also in the vicinity of the toner temperature T in the second nip region N2, and high adhesion is achieved. It can be secured. As described above, when the fixing process is performed in the vicinity of the toner temperature T where the adhesive force between the toner and the fixing belt is strong, and the sheet is separated from the fixing belt 43, a high-quality image with very little uneven gloss can be obtained.

  Further, the width of the first nip region N1 is preferably not more than twice the width of the second nip region N2. Thus, the toner can be melted in the first nip region N1, and the effect of assisting the toner in close contact with the fixing belt can be exhibited in the second nip region N2, and the adhesion in the second nip region N2 can be further enhanced. it can.

  Further, it is preferable that the difference between the first temperature of the fixing belt 43 at the start of the nip portion N and the second temperature of the fixing belt 43 at the separation / contact position of the sheet by the separating member 44 is less than 10 ° C. As described above, when the temperature difference between the first temperature and the second temperature is small, the adhesive force of the toner to the fixing belt can be maintained in the second nip region N2, so that the adhesion between the sheet and the fixing belt can be ensured. Further, since the temperature decrease of the fixing belt 43 is small, the toner temperature is also hardly decreased, and the sheet can be separated from the fixing belt at an appropriate toner temperature.

[Second Embodiment]
Next, a fixing device 91 in which only the configuration of the separation member 44 of the fixing device 40 according to the first embodiment of the present invention is changed will be described. Parts corresponding to those of the fixing device 40 according to the first embodiment of the present invention are denoted by the same reference numerals, and description thereof is omitted to avoid duplication.

  FIG. 4 is a schematic cross-sectional view showing the configuration of the fixing device 91 according to the second embodiment of the present invention. A separation member (separation roller) 86 provided in the fixing device 91 according to the present embodiment is a driven roller that is rotatably provided and rotates following the endless rotation of the fixing belt 43. With such a separation roller 86, the sliding load is reduced, and damage to the fixing belt 43 and the separation member 44 can be suppressed.

  The separation roller 86 is provided downstream of the fixing roller 41 in the paper conveyance direction P and away from the fixing roller 41 and the pressure roller 42. Further, the separation roller 86 is arranged so that at least a part thereof is closer to the pressure roller 42 than a tangent line connecting the start end and the end of the first nip region N1. The separation roller 86 separates the fixing belt 43 from the fixing roller 41, and a portion where the pressure roller 42 is in contact with the outer peripheral surface of the fixing belt 43 is formed. This portion corresponds to the second nip region. That is, in the second nip region N2, the separation roller 86 provided away from the fixing roller 41 and the pressure roller 42 is disposed closer to the pressure roller 42 than a tangent line connecting the start end and the end of the first nip region N1. This is a region formed by doing so. Therefore, since the fixing belt 43 is pressed against the pressure roller 42 by the separation roller 86, the deflection of the fixing belt 43 in the second nip region N2, that is, the occurrence of so-called pressure loss can be suppressed.

  The outer diameter of the separation roller 86 is not particularly limited, and is appropriately set depending on the situation, but is preferably 4 to 8 mm, for example, 6 mm. The material of the separation roller 86 is not particularly limited, and examples thereof include those in which the surface of SUS is ceramic coated.

[Third Embodiment]
In the first and second embodiments, the fixing device in which the fixing roller is a heating roller that heats the fixing belt has been described. However, a fixing device in which the fixing roller and the heating roller are composed of separate rollers, a so-called melt. A type fixing device will be described. Portions corresponding to those of the fixing devices according to the first and second embodiments of the present invention are denoted by the same reference numerals, and description thereof is omitted to avoid duplication.

  FIG. 5 is a schematic cross-sectional view showing the configuration of the fixing device 92 according to the third embodiment of the present invention. In the fixing device 92 according to this embodiment, the fixing belt 43 is stretched around a fixing roller 88, a separation roller 86, and a heating roller 87.

  The fixing roller 88 is disposed so as to be oriented to the pressure roller 42 via the fixing belt 43. The fixing roller 88 is not particularly limited, but is preferably an elastic roller provided with an elastic layer. A preferable specific example of the fixing roller 88 is, for example, an elastic roller made of a silicone sponge. When such an elastic roller is used, the elastic layer is deformed by being pressed by the pressure roller 42 and the nip width can be increased. Further, since the fixing roller 88 is not a heating roller, problems such as a long warm-up time and a decrease in temperature followability during continuous paper feeding due to the elastic layer do not occur. The outer diameter of the fixing roller 88 is not particularly limited and is appropriately set depending on the situation, but may be relatively thinner than the fixing roller 41 of the first and second embodiments. It is preferable that it is 40 mm, for example, it sets to 30 mm.

  As the heating roller 87, a roller having the same configuration as the fixing roller 41 of the first embodiment and the second embodiment can be used. The outer diameter of the heating roller 87 is not particularly limited and is appropriately set according to the situation. However, since it is not necessary to consider securing the nip width, the outer diameter of the first embodiment and the second embodiment is not limited. It may be relatively thinner than the fixing roller 41, and is preferably 20 to 40 mm, for example, set to 30 mm.

  As described above, since the fixing device 92 according to the third embodiment includes the heating roller 87 in addition to the fixing roller 88, the fixing roller 88 can be an elastic roller suitable for the fixing process.

  Note that the fixing device 92 according to the third embodiment is not provided with a tension roller, but may be provided. When no tension roller is provided, the heating roller 87 may have a function of applying tension so that the fixing belt 43 does not loosen. The fixing device 92 according to the third embodiment does not include a thermistor, but may provide it.

[Fourth Embodiment]
In the first embodiment and the second embodiment, the fixing device provided with the tension roller has been described. However, the fixing device that does not include the tension roller by changing the configuration of the separating member will be described. Portions corresponding to those of the fixing devices according to the first and second embodiments of the present invention are denoted by the same reference numerals, and description thereof is omitted to avoid duplication.

  FIG. 6 is a schematic cross-sectional view showing a configuration of a fixing device 93 according to the fourth embodiment of the present invention.

  The separation member 89 provided in the fixing device 93 according to the present embodiment is the same as the separation member 44 of the first embodiment, except that it has a function of applying tension so that the fixing belt 43 does not loosen. In this way, by using the separating member 89 having a function of applying tension, it is not necessary to provide a tension roller, and the size can be reduced. Further, such a small fixing device can further reduce the warm-up time because the heat capacity of the entire device is reduced.

1 is a schematic cross-sectional view illustrating an overall configuration of a color printer 1 including a fixing device 40 according to a first embodiment of the present invention. 1 is a schematic cross-sectional view illustrating a configuration of a fixing device 40 according to a first embodiment of the present invention. 6 is a graph showing a relationship between an adhesive force between a toner and a fixing belt and a toner temperature. FIG. 6 is a schematic cross-sectional view illustrating a configuration of a fixing device 91 according to a second embodiment of the present invention. FIG. 9 is a schematic cross-sectional view illustrating a configuration of a fixing device 92 according to a third embodiment of the present invention. FIG. 6 is a schematic cross-sectional view illustrating a configuration of a fixing device 92 according to a fourth embodiment of the present invention. FIG. 6 is a schematic cross-sectional view illustrating a configuration of a conventional fixing device 101.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color printer 2 Paper feed part 3 Image forming part 4 Fixing part 5 Paper discharge part 40, 91, 92, 93 Fixing device 41, 88 Fixing roller 42 Pressure roller 43 Fixing belt 44, 89 Separating member 45 Tension roller 46 Thermistor 47 Front guide plate 48 Rear guide plate 81, 83 Metal roller 82, 85 Halogen lamp 84 Silicone rubber layer 86 Separating roller 87 Heating roller

Claims (13)

An endless fixing belt that is stretched over a plurality of support members and rotates;
A pressure roller that contacts the outer peripheral surface of the fixing belt and forms a nip portion;
The plurality of support members include a fixing roller facing the pressure roller via the fixing belt,
A sheet separating member provided on the downstream side in the sheet conveying direction from the fixing roller and separated from the fixing roller and the pressure roller;
The nip portion includes a first nip region N1 that contacts the fixing roller, and a second nip region N2 that continues downstream of the first nip region N1 in the sheet conveyance direction,
The fixing device, wherein a width of the first nip region N1 is equal to or greater than a width of the second nip region N2.   The fixing device according to claim 1, wherein a radius of curvature of the fixing belt at a portion in contact with the separation member is smaller than a radius of the fixing roller.   The fixing device according to claim 1, wherein the fixing roller is a heating roller that heats the fixing belt. The plurality of support members include the fixing roller as an elastic roller, and a heating roller,
The fixing belt is stretched over the fixing roller, the heating roller, and the separation member,
The fixing device according to claim 1, wherein the heating roller heats the fixing belt.   5. The fixing device according to claim 1, wherein a width of the first nip region N <b> 1 is not more than twice a width of the second nip region N <b> 2.   The fixing device according to claim 1, wherein the separation member is a fixed guide member having a sliding contact surface that is in sliding contact with the fixing belt.   The fixing device according to claim 1, wherein the separation member is a driven roller that rotates following the rotation of the fixing belt.   8. The difference between the first temperature of the fixing belt at the start end of the nip portion and the second temperature of the fixing belt at the position where the sheet is separated by the separation member is less than 10 ° C. 8. The fixing device according to Item 1.   The fixing device according to claim 1, wherein the fixing belt is a member having a large heat capacity.   The fixing device according to claim 9, wherein the fixing belt is a belt made of a member including a nickel layer or a member having a silicone rubber layer on a surface thereof.   The fixing device according to claim 1, wherein the separation member is a member made of a heat insulating material having a heat insulating property or a member covered with a heat insulating material having a heat insulating property.   The fixing device according to claim 1, wherein the pressure roller is a driving roller that drives the fixing belt. An image forming apparatus using an electrophotographic method,
An image forming apparatus comprising the fixing device according to claim 1.

Images